Controlling electrical device based on temperature and voltage

ABSTRACT

In an embodiment, a lifetime controller is configured to monitor operating conditions for a device, and to control operating conditions based on the previous conditions to improve the reliability characteristics of the device while permitting strenuous use as available. For example, the lifetime controller may permit strenuous use when the device is first powered on. Once a specified amount of strenuous use has occurred, the controller may cause the operating conditions to be reduced to reduce the wear on the device, and thus help to extend the lifetime of the device. Similarly, if a device is used in less strenuous conditions, the controller may accumulate credit which may be expended by permitting the device to operate in more strenuous conditions for a period of time.

BACKGROUND Technical Field

Embodiments described herein are related to lifetime management for anelectronic device.

Description of the Related Art

Electronic devices are typically designed to a target service lifetime,during which the device is expected to operate correctly. Beyond thisservice lifetime, the device may fail to operate correctly due to wearor other common aging effects. While a given instance of a device mayhave a defect that causes the device to fail before the lifetime,generally the failure rate prior to the end of the lifetime is expectedto be on the order of one in several million instances.

Reliability analysis generally has to do with determining the worst caseconditions that can cause the device to fail, and ensuring that thecomponents of the device will not fail more often than the desiredfailure rate over the desired lifetime under those worst caseconditions. Such determinations are intentionally conservative, and thusnumerous devices that do not frequently experience worst-case conditionsmay have lifetimes that far exceed the design lifetime. While theadditional lifetime can be welcome, it can also indicate at the deviceis over-engineered and possibly more expensive than necessary.

SUMMARY

In an embodiment, a lifetime controller is configured to monitoroperating conditions for a device, and to control operating conditionsbased on the previously detected conditions to improve the reliabilitycharacteristics of the device while permitting strenuous use asavailable. For example, the lifetime controller may permit strenuous usewhen the device is first powered on. Once a specified amount ofstrenuous use has occurred, the controller may cause the operatingperformance to be reduced to limit the wear on the device, and thus helpto extend the lifetime of the device. Similarly, if a device is used inless strenuous conditions, the controller may accumulate credit whichmay be expended by permitting the device to operate in more strenuousconditions for a period of time. By controlling the device in thisfashion, a low lifetime failure rate for a set of devices may bemaintained while permitting strenuous operation of the device (whichcould cause wear) for at least some periods of time to satisfy userdemands.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description makes reference to the accompanyingdrawings, which are now briefly described.

FIG. 1 is a block diagram of a system implementing one embodiment oflifetime control.

FIG. 2 is a flowchart illustrating one embodiment of lifetime control inthe system of FIG. 1.

FIG. 3 is a flowchart illustrating another embodiment of lifetimecontrol in the system of FIG. 1.

FIG. 4 is a graph illustrating one embodiment of lifetime control as afunction of time.

FIG. 5 is a graph illustrating another embodiment of lifetime control asa function of time.

FIG. 6 is an embodiment of a table of acceleration factors.

FIG. 7 is a block diagram of one embodiment of a computer accessiblestorage medium.

While embodiments described in this disclosure may admit to variousmodifications and alternative forms, specific embodiments thereof areshown by way of example in the drawings and will herein be described indetail. It should be understood, however, that the drawings and detaileddescription are not intended to limit the embodiments to the particularform disclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the appended claims. The headings used herein are fororganizational purposes only and are not meant to be used to limit thescope of the description. As used throughout this application, the word“may” is used in a permissive sense (i.e., meaning having the potentialto), rather than the mandatory sense (i.e., meaning must). Similarly,the words “include”, “including”, and “includes” mean including, but notlimited to.

Various units, circuits, or other components may be described as“configured to” perform a task or tasks. In such contexts, “configuredto” is a broad recitation of structure generally meaning “havingcircuitry that” performs the task or tasks during operation. As such,the unit/circuit/component can be configured to perform the task evenwhen the unit/circuit/component is not currently on. In general, thecircuitry that forms the structure corresponding to “configured to” mayinclude hardware circuits and/or memory storing program instructionsexecutable to implement the operation. The memory can include volatilememory such as static or dynamic random access memory and/or nonvolatilememory such as optical or magnetic disk storage, flash memory,programmable read-only memories, etc. Similarly, variousunits/circuits/components may be described as performing a task ortasks, for convenience in the description. Such descriptions should beinterpreted as including the phrase “configured to.” Reciting aunit/circuit/component that is configured to perform one or more tasksis expressly intended not to invoke 35 U.S.C. § 112(f) interpretationfor that unit/circuit/component.

This specification includes references to “one embodiment” or “anembodiment.” The appearances of the phrases “in one embodiment” or “inan embodiment” do not necessarily refer to the same embodiment, althoughembodiments that include any combination of the features are generallycontemplated, unless expressly disclaimed herein. Particular features,structures, or characteristics may be combined in any suitable mannerconsistent with this disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

In various embodiments, a system may include an electrical device forwhich lifetime is to be managed. The electrical device may be anydevice. For example, the electrical device may include any of thefollowing in some embodiments an integrated circuit, two or moreintegrated circuits, one or more integrated circuits mounted on a boardwith one or more other components, etc. The electrical device may bepart of a product or the entire product, in various embodiments. Theelectrical device may have one or more operating parameters that aremonitored to manage lifetime. Operating parameters may be any data thatrepresents the operating conditions of the device. Exemplary parametersmay include one or more supply voltage magnitudes, one or more supplycurrent magnitudes, one or more operating temperatures, one or moreoperating clock frequencies, etc. Embodiments including a particularelectrical device and operating parameters thereof are described in moredetail as an example below, but any device and parameters may be used inother embodiments.

FIG. 1 is a block diagram of one embodiment of a system including anelectrical device 10, a closed loop thermal management (CLTM) controller12, an acceleration factor generator 14, and a lifetime controller 16.In the illustrated embodiment, the acceleration factor generator 14 iscoupled to receive one or more operating parameters from the device 10and is configured to generate an instantaneous acceleration factor(AF_(i)). The lifetime controller 16 is coupled to receive a differencebetween a target acceleration factor (AF_(T)) and the instantaneousacceleration factor (AF_(i)). Optionally, the lifetime controller 16 maybe coupled to receive an initial credit. The lifetime controller isconfigured to provide various constraints and/or control data (e.g. amaximum die temperature, MaxT_(d)) to the CLTM controller 12, which isconfigured to provide one or more controls to the device 10. Theconstraints/control data may be generically referred to as “controlparameters.”

In the embodiment of FIG. 1, the device 10 includes an integratedcircuit implementing a system on a chip (SOC) 18, a memory 20, a powermanagement unit (PMU 22), and one or more peripheral devices 24. The SOC18 may include a memory controller 26, one or more processors 28, andone or more peripheral components 30. The SOC 18 may further include oneor more temperature sensors 32, and the device 10 may further includeother temperature sensors such as the temperature sensor 34.

In the illustrated embodiment, the monitored operating parameters forlifetime management include the operating temperature (T) and supplyvoltage magnitude (V). The operating temperature may be measured (e.g.via temperature sensors 32 and/or 34). In one embodiment, the operatingtemperature may be the die temperature of the SOC 18 (that is, thetemperature of the semiconductor substrate in which the SOC 18 isfabricated, as measured by the temperature sensor(s) 32). Otheroperating temperatures may include the external temperature of the SOC18 (e.g. the temperature of the package of the SOC 18), the temperatureof other components such as the PMU 22, the peripheral devices 24, thedevice 10 as a whole, etc.). Combinations of various operatingtemperatures may be used (e.g. an average of several measuredtemperatures from different points in the device 10). In an embodiment,one or more of the temperatures may be synthesized from other dataavailable to the system. For example, the system may have a model ofdevice thermal transfer characteristics that allows it to calculate anoperating temperature from indirect measurements such as input power.The supply voltage magnitude may be a setting in the PMU 22, and thusneed not be measured using a sensor, but rather may be recorded. Theactual instantaneous supply voltage magnitude may vary due to loading,noise, etc. but may generally be targeted at the supply voltagemagnitude setting. Accordingly, the monitored operating parameters maybe either measured or recorded from a setting, or any combinationthereof.

The acceleration factor generator 14 may receive the monitoredparameters and may be configured to generate the instantaneousacceleration factor. The acceleration factor may represent how quicklythe values of the monitored operating parameters may lead to end of life(failure) of the device 10. In an embodiment, the acceleration factormay be normalized to nominal values for the operating parameters. Thatis, the nominal values may be values at which the device 10 may operatecontinuously over its lifetime without experiencing failure ratesgreater than a specified target. There may be multiple nominal values(e.g. a curve on a graph of the operating parameters, which in oneembodiment may be a straight line). The acceleration factor for thenominal values may be about 1. Values of the operating parameters thatare more strenuous than the nominal values (e.g. values that are morelikely to cause wear or damage to the device) may have accelerationfactors greater than 1 and values of the operating parameters that areless strenuous than the nominal values may have acceleration factorsless than 1.

In an embodiment, the target acceleration factor to which theinstantaneous acceleration factor is compared may be 1. That is, overtime, the instantaneous acceleration factor may be controlled towardthis target. Periods of high stress (acceleration factors greaterthan 1) may be offset by periods of low stress (acceleration factorslower than 1) to arrive at the desired lifetime. The lifetime controllermay accumulate credit during periods of low stress and may allow thatcredit to be consumed in periods of high stress before controlling thedevice 10 to prevent premature failure.

In another embodiment, the lifetime controller 16 may be initialized atboot with an initial credit. The initial credit represents credit thatthe lifetime controller 16 may consume even if the controller 16 has notyet detected less strenuous operation. The availability of the initialcredit may permit early, high performance operation (which may enhancethe user experience). To offset the initial credit, the targetacceleration factor (AF_(T)) may be computed to be less than one. Thatis, the target acceleration factor AF_(T) may recover the consumedcredit represented by the initial credit.

Based on the difference between the target acceleration factor and theinstantaneous acceleration factor, the lifetime controller 16 may beconfigured to generate control parameters for the operation of thedevice 10. The control parameters may serve as constraints on the deviceoperation. That is, the device 10 may operate up to the constraint, butnot exceed the constraint. Operation within the constraint (i.e. notapproaching the constraint) is also permitted. The constraint may beplaced on one or more operating parameters of the device 10. Forexample, in the illustrated embodiment, the constraint may be on theoperating temperature (and specifically the die temperature of the SOC18). The constraint may be placed on an operating parameter that is notmonitored by the acceleration factor generator 14, in some embodiments.In other embodiments, the constraint may be placed on an attribute otherthan an operating parameter (e.g. maximum continuous up time, which is ameasurement of a maximum time that the SOC 18 is permitted to beactively executing before a sleep or power down time is desired).

The control parameters generated by the lifetime controller 16 maydirectly control the operation of the device 10, in some embodiments. Inthe illustrated embodiment, the control parameters may indirectlycontrol operation of the device 10 by providing a constraint to anothercontroller (the CLTM controller 12 in this example). The lifetimecontroller 16 may generate a maximum temperature constraint, forexample. If the lifetime controller 16 determines that performance is tobe limited to enhance lifetime, a lower maximum temperature may begenerated. If credit is available, a higher maximum temperature may begenerated. Other embodiments may control other aspects of the device 10(e.g. processor operating frequency, operating frequencies of othercomponents, supply voltage magnitude, etc.). Combinations of constraintsmay be used. Generally, credits may be accumulated when the differencebetween the target acceleration factor and the instantaneousacceleration factor is positive and consumed when the difference isnegative.

More particularly in one embodiment, the lifetime controller 16 may beconfigured to control operation of the device 10 based on theacceleration factor difference and a history of previous differences.For example, the lifetime controller 16 may implementproportional-integral (PI) control. The integral portion of thecontroller 16 may accumulate the credits and may be initialized with theinitial credits.

In one embodiment, the history of acceleration factor differences may bea history since the device was first placed into service (e.g. since theinitial boot of the device 10 by the user, after purchase of the device10 from the manufacturer by the user, or the time since the device wasmanufactured). To track history in such embodiments, the history may besaved when the device 10 is powered off. The history may be saved innon-volatile memory in the device 10, for example. Alternatively or inaddition, the history may be saved external to the device 10 (e.g. inthe “cloud,” on a server to which the device 10 may be connected, on acomputer to which the device is periodically synchronized, etc.). Savingthe history externally may be used to ensure that the history isretained if the device 10 is reset to factory settings due to a softfailure, corruption of device data, etc. In such embodiments, theinitial credit at first boot may be a total initial credit. Insubsequent boots, the initial credit may restore the credit (or deficit)from the saved history.

In another embodiment, the history of acceleration factor differencesmay be a history since the most recent boot of the device 10. Suchembodiments need not attempt to store the history across power downevents in the device 10. In such an embodiment, the initial credit ateach boot may be a credit determined from a total credit allocated toinitial credits and an expected number of lifetime boots of the device10. For example, if the device 10 is expected to boot about 500 timesover its service lifetime, the initial credit at each boot may be thetotal allocated credit divided by 500. It is noted that 500 boots isonly an example provided for illustration; the expected number oflifetime boots may be higher or lower than the example of 500 boots.

The CLTM controller 12 may be provided to control the device 10 based onthe current temperature and a maximum (or control target) temperature.In the absence of the lifetime controller 16, the CLTM controller 12 maybe provided a maximum temperature that is static and is based on thechance of immediate failure (not lifetime failure), comfortable use ofthe device (e.g. a handheld device may not be permitted to get hotenough that holding the device causes discomfort or injury), etc. TheCLTM controller 12 may be configured to provide a variety of controls invarious embodiments. For example, supply voltages and/or clockfrequencies may be reduced to reduce operating temperature. Power statesmay be changed to use different voltage/frequency pairs that may causeless wear on the device 10. Amount of active operation per unit time maybe varied (e.g. amount of active execution in the processors 28). TheCLTM controller 12 may receive the temperature measurements as well, forcomparison of the measured temperature to the maximum temperature. It isnoted that one or both of the CLTM controller 12 and the lifetimecontroller 16 may be implemented in software executed on one or more ofthe processors included in the SOC 18 and/or in hardware.

The SOC 18, as mentioned previously, may be a single semiconductorsubstrate on which many system components may be integrated. Theprocessors 28 may include circuitry that implements an instruction setarchitecture, and thus may execute programs coded to the instruction setarchitecture employed by the processors. The processors may have anyconstruction and design, included in-order or out-of-order execution,superscalar architecture, pipelined design, etc. Generally, a processormay include any circuitry and/or microcode configured to executeinstructions defined in the instruction set architecture. Processors mayencompass processor cores implemented on an integrated circuit withother components as a system on a chip (SOC 18) or other levels ofintegration. Processors may further encompass discrete microprocessors,processor cores and/or microprocessors integrated into multichip moduleimplementations, processors implemented as multiple integrated circuits,etc. The processors may include general purpose processors (sometimesreferred to as “application processors”) or task-specific processors.The task-specific processors may be processors optimized for thespecific tasks (e.g. digital signal processors or graphics processingunits). The task-specific processors may also be smaller, lowerperformance general purpose processors provided to execute the softwareforming the specific task.

The peripheral components 30 may be on-chip peripherals, as compared tothe peripheral devices 24 that may be off-chip. Any set of on-chipperipheral components may be included. For example, various imageprocessing and display peripherals may be included (e.g. image signalprocessors, cameras, display controllers, graphics processing units(GPUs), etc.). Audio processing peripherals (e.g. digital signalprocessors (DSPs) and audio processing hardware) may be included.Compression/decompression units (e.g. audio/video compression anddecompression) may be included. Audio/video coder/decoders (codecs) maybe included. Network peripherals may be included. Peripheral components30 that control external interfaces to peripheral devices 24 or othercircuitry may in the device 10 may be included.

The memory controller 26 may include circuitry to interface to thememory 20 on behalf of the processors 28, the peripheral components 30,and various other circuitry in the SOC 18 and/or device 10. Any type ofmemory 20 may be supported. For example, the memory 20 may be staticrandom access memory (SRAM), dynamic RAM (DRAM) such as synchronous DRAM(SDRAM) including double data rate (DDR, DDR2, DDR3, DDR4, etc.) DRAM.Low power/mobile versions of the DDR DRAM may be supported (e.g. LPDDR,mDDR, etc.). The memory controller 26 may include queues for memoryoperations, for ordering (and potentially reordering) the operations andpresenting the operations to the memory 20. The memory controller 26 mayfurther include data buffers to store write data awaiting write tomemory and read data awaiting return to the source of the memoryoperation.

The temperature sensors 32 and 34 may be any type of sensor that reactsin a detectable, predictable way to changes in temperature. Thetemperature sensors 32 may be implemented on chip in the SOC 18, whilethe temperature sensors 34 may be discrete sensors included in thesystem. Any number of on-chip and/or off-chip sensors may be used invarious embodiments.

The peripheral devices 24 may be any other components that may beincluded in the device 10. For example, radio chips for wirelesslocal-area networking (WLAN or “Wi-Fi™”), cellular communications, etc.may be included. Various other types of sensors such as any number of:an accelerometer, a gyroscope (or gyro), a magnetometer, an audiodetector (e.g. a microphone), a photodetector that detects light orother electromagnetic energy, an altimeter, a pressure sensor, etc. Userinterface devices such as a button, a touch screen, a keyboard, apointing device, a camera, etc. may also be peripheral devices 24.

The PMU 22 may be configured to supply various supply voltages to theSOC 18, the memory 20, and/or the peripheral devices 24. The PMU 22 maybe programmable to enable/disable the supply voltages and may beprogrammable with the selected supply voltage magnitudes for eachsupply.

FIG. 2 is a flowchart illustrating operation of one embodiment of theacceleration factor generator 14 and the lifetime controller 16 in whichstate is saved between boots. While the blocks are shown in a particularorder for ease of understanding in FIG. 2, other orders may be used.Operations represented by blocks may also be performed in parallel. Theacceleration factor generator 14 and the lifetime controller 16 may beconfigured to implement the operation shown in FIG. 2.

The operation illustrated in the flowchart begins at the boot of thedevice 10. If the device 10 is performing its initial boot (decisionblock 40, “yes” leg), the lifetime controller 16 may be configured toload the initial credit (block 42). The initial credit may be providedin a predefined location in the device 10, for example. In anotherembodiment, the initial credit may be coded into the lifetime controller16 or may be provided from an external source to which the device 10 mayconnect. If the device 10 is not performing its initial boot (decisionblock 40, “no” leg), the saved state from the most recent shutdown maybe loaded (block 44).

During operation, at various points in time, a temperature sample may betaken. For example, a temperature sample may be taken once every 5seconds. Shorter or longer intervals may be used in other embodiments.In response to a temperature sample (decision block 46, “yes” leg), theacceleration factor generator 14 may be configured to generate theinstantaneous acceleration factor (AF_(i)) based on the sampledtemperature and the supply voltage magnitude (block 48). The lifetimecontroller 16 may generate the maximum die temperature (MaxT_(d))responsive to a difference between AF_(i) and AF_(T) as well as ahistory of the differences, as represented by the initial credit/stateload at boot and the subsequent temperature samples (block 50). If a newtemperature has not been received (decision block 46, “no” leg), blocks48 and 50 may be skipped.

If a shutdown event occurs (decision block 52, “yes” leg), the lifetimecontroller 16 may be configured to save the state representing theaccumulated history of AF_(i)/AF_(T) differences (block 54). The statemay then be available for reload at the next boot. A shutdown event mayoccur when the device 10 is being powered off. For example, a shutdownevent may be responsive to a user interaction. A shutdown event may beresponsive to a measurement of unsafe device temperature. A shutdownevent, for portable devices operating from a battery, may be responsiveto low battery power.

FIG. 3 is a flowchart illustrating operation of one embodiment of theacceleration factor generator 14 and the lifetime controller 16 in whichstate is not saved between boots. While the blocks are shown in aparticular order for ease of understanding, other orders may be used.Operations represented by blocks may also be performed in parallel. Theacceleration factor generator 14 and the lifetime controller 16 may beconfigured to implement the operation shown in FIG. 3.

The operation of the flowchart may begin at the boot of the device 10.Because there is no saved state in this embodiment, the lifetimecontroller 16 may load the initial credit on each boot (block 60).

During operation, at various points in time, a temperature sample may betaken as mentioned above in the embodiment of FIG. 2. In response to atemperature sample (decision block 46, “yes” leg), the accelerationfactor generator 14 may be configured to generate the instantaneousacceleration factor (AF_(i)) based on the sampled temperature and thesupply voltage magnitude (block 48). The lifetime controller 16 maygenerate the maximum die temperature (MaxT_(d)) responsive to adifference between AF_(i) and AF_(T) as well as a history of thedifferences, as represented by the initial credit/state load at boot andthe subsequent temperature samples (block 50). If a new temperaturesample has not been received (decision block 46, “no” leg), blocks 48and 50 may be skipped. If a shutdown event occurs (decision block 52,“yes” leg), no state is saved in this embodiment.

Turning now to FIG. 4, a graph is shown illustrating one embodiment ofacceleration factors over time to reach a at least a targeted lifetime.In the graph of FIG. 4, time is illustrated on the horizontal axis, withunits increasing from left to right from initial boot on the left untilthe targeted lifetime is reached on the right. On the vertical axis, theintegral of the acceleration factor is shown, from 0 to the lifetimeamount. Controlled as described herein by the lifetime controller 16 ineach device 10, a set of devices 10 may reach the targeted lifetime witha low failure rate (e.g. on the order of one in millions of devices).The lifetime controller 16 may permit high performance use of thedevices 10 when credit is available, which may provide a better userexperience at times of high stress use, while still maintaining a lowfailure rate. For a given device 10, the lifetime controller 16 mayreduce the risk of failure and thus may lead to an extended life ascompared to unconstrained operation.

Operation in the absence of an initial credit is illustrated via thestraight lower line 70 on the graph. The line 70 has a unit slope, andthus AF_(T)=1. That is, if the average acceleration factor over the lifeof the device is 1, the device 10 should reach the lifetime with aspecified failure rate. The actual AF_(i) experienced throughout thelife of the device may vary from AF_(T), but the lifetime controller maycontrol AF_(i) over time to approximate AF_(T) (or at least to avoidexceeding AF_(T), on average, over time).

Also illustrated in FIG. 4 is a curve that may result from the use ofinitial credits. In the illustrated embodiment, a line 72 that issteeper than the no initial credit line 70 may be permitted initially.The slope of the line 72 is greater than AF_(T) because the initialcredits permit the operation at greater than AF_(T) until the credit isexhausted. At a certain time (dotted line 76), the initial credit isconsumed. The slope of the curve reduces to AF_(T) (line 74), which iscalculated so that operation over the remaining life concludes at thespecified failure rate.

FIG. 5 is another graph corresponding to the embodiment of FIG. 3. Inthis embodiment, a portion of the total allocated initial credit isprovided after each reboot. Accordingly, at each reboot, a steep sectionof the curve 78 is provided followed by a shallower slope 80.

In an embodiment, the acceleration factor generator 14 may be configuredto use a lookup table to convert input temperatures and supply voltagemagnitudes to acceleration factors. FIG. 6 is a block diagram of oneembodiment of such a table 82. The entries in the table 82 may bepopulated according to simulation results over the design of the device10 in various conditions, based on specifications for the components ofthe device 10, or by other methods. In cases in which atemperature-voltage combination does not explicitly appear in the table82, interpolation between the values in the table entries may be used todetermine AF_(i).

As mentioned previously, the acceleration factors may be normalized tonominal values. The nominal values may lie along a line near thediagonal 84 from the lower left to the upper right of the table 82. Thevalues in this region of the table may thus be near 1. Lower supplyvoltage magnitudes and lower temperatures may both induce lesswear/damage in the monitored components, and thus entries in the upperleft region of the table, above the diagonal 84 may be smallacceleration factors (i.e. less than 1)—reference numeral 86 in FIG. 6.Similarly, higher voltage magnitudes and/or temperatures may result inhigher acceleration factors above the diagonal 84 (i.e. greater thanone)—reference numeral 88 in FIG. 6.

FIG. 7 is a block diagram of one embodiment of a computer accessiblestorage medium 200. Generally speaking, a computer accessible storagemedium may include any storage media accessible by a computer during useto provide instructions and/or data to the computer. For example, acomputer accessible storage medium may include storage media such asmagnetic or optical media, e.g., disk (fixed or removable), tape,CD-ROM, DVD-ROM, CD-R, CD-RW, DVD-R, DVD-RW, or Blu-Ray. Storage mediamay further include volatile or non-volatile memory media such as RAM(e.g. synchronous dynamic RAM (SDRAM), Rambus DRAM (RDRAM), static RAM(SRAM), etc.), ROM, or Flash memory. The storage media may be physicallyincluded within the computer to which the storage media providesinstructions/data. Alternatively, the storage media may be connected tothe computer. For example, the storage media may be connected to thecomputer over a network or wireless link, such as network attachedstorage. The storage media may be connected through a peripheralinterface such as the Universal Serial Bus (USB). Generally, thecomputer accessible storage medium 200 may store data in anon-transitory manner, where non-transitory in this context may refer tonot transmitting the instructions/data on a signal. For example,non-transitory storage may be volatile (and may lose the storedinstructions/data in response to a power down) or non-volatile.

The computer accessible storage medium 200 in FIG. 7 may store codeforming the lifetime controller 16, the acceleration factor generator14, and/or the CLTM controller 12. The computer accessible storagemedium 200 may still further store the saved state 202 (e.g. theaccumulated credit from previous operation), as mentioned above withregard to FIG. 2. The lifetime controller 16 may include instructionswhich, when executed by the processor 28, implement the operationdescribed for the lifetime controller 16 above. The acceleration factorgenerator 14 may include instructions which, when executed by theprocessor 28, implement the operation described for the accelerationfactor generator 14 above. The CLTM controller 12 may includeinstructions which, when executed by the processor 28, implement theoperation described for the CLTM controller 12 above. Alternatively, oneor more of the above may be implemented partially in hardware andpartially in instructions executed by the processor 28. A carrier mediummay include computer accessible storage media as well as transmissionmedia such as wired or wireless transmission.

Numerous variations and modifications will become apparent to thoseskilled in the art once the above disclosure is fully appreciated. It isintended that the following claims be interpreted to embrace all suchvariations and modifications.

What is claimed is:
 1. A system comprising: an electrical deviceoperating responsive to a supply voltage during use, wherein theelectrical device includes one or more temperature sensors that measureoperating temperatures in the electrical device to generate an operatingtemperature measurement during use; an acceleration factor generatorcoupled to receive the operating temperature measurement and a magnitudeof the supply voltage, wherein, during use, the acceleration factorgenerator determines an instantaneous acceleration factor measuring acurrent acceleration of end of life experienced by the electricaldevice; a first controller coupled to receive a difference between atarget acceleration factor and the instantaneous acceleration factor,wherein the target acceleration factor is calculated to result in nomore than a targeted failure rate over a targeted lifetime, wherein thefirst controller generates one or more controls to constrain operationof the electrical device responsive to a history of the differenceduring use; and a second controller coupled to the first controller andto the electrical device, wherein the second controller constrains theoperation of the electrical device during use responsive to the one ormore controls from the first controller.
 2. The system as recited inclaim 1 wherein the history is gathered since a most recent reboot ofthe system.
 3. The system as recited in claim 1 wherein the history isgathered since an initial boot of the system.
 4. The system as recitedin claim 1 wherein the one or more controls comprise a maximum operatingtemperature for the electrical device.
 5. The system as recited in claim1 wherein the first controller accumulates credit responsive to thedifference being positive during use, and wherein the first controllerpermits less constrained operation responsive to the accumulated creditduring use.
 6. The system as recited in claim 1 wherein the firstcontroller initializes a credit during boot of the system, and whereinthe first controller permits less constrained operation responsive tothe credit during use.
 7. A method comprising: detecting one or moreoperating parameters of an electrical device, wherein an operatingtemperature of a semiconductor substrate in an integrated circuit withinthe electrical device is one of the operating parameters; generating,responsive to the one or more operating parameters, an accelerationfactor that represents an acceleration of an end of life of theelectrical device with respect to values of the one or more operatingparameters at which the electrical device is expected to meet a definedfailure rate at a defined end of life; generating, responsive to theacceleration factor and a target acceleration factor, one or moreconstraints for operation of the electrical device; and operating theelectrical device within the constraints to preserve the defined end oflife.
 8. The method as recited in claim 7 wherein a supply voltagemagnitude is another one of the operating parameters.
 9. The method asrecited in claim 7 wherein the acceleration factor and the targetacceleration factor are normalized to values of the one or moreoperating parameters at which the electrical device is operablecontinuously over its lifetime to meet the defined end of life.
 10. Themethod as recited in claim 7 wherein generating the one or moreconstraints permit operation at greater than the normalized valueresponsive to a credit in the constraint generation.
 11. The method asrecited in claim 10 wherein the credit is an initial credit loaded atinitialization of the electrical device.
 12. The method as recited inclaim 11 wherein the target acceleration factor is calculated to offsetthe initial credit.
 13. The method as recited in claim 10 furthercomprising accumulating the credit responsive to operating theelectrical device at less than the constraints.
 14. A non-transitorycomputer accessible storage medium storing a plurality of instructionswhich, when executed by a processor in an electrical device: receive adifference between a target acceleration factor determined to preventpremature end of life for the electrical device and an instantaneousacceleration factor; generate one or more constraints for the operationof the electrical device responsive to the difference; and constrain theoperation of the electrical device responsive to the constraints,wherein the constraints permit operation of the electrical circuit abovea point at which continuous operation is possible to reach the end oflife responsive to a credit accumulated due to the instantaneousacceleration factor being less than the target acceleration factor forone or more previous samples of the instantaneous acceleration factor.15. The non-transitory computer accessible storage medium as recited inclaim 14 wherein the instructions, when executed, load an initial creditduring initialization of the electrical system, wherein the initialcredit causes generation of constraints that permit operation of theelectrical circuit above a point at which continuous operation ispossible to reach the end of life.
 16. The non-transitory computeraccessible storage medium as recited in claim 14 wherein the pluralityof instructions, when executed, save state that represents a history ofthe differences prior to the electrical device shutting down.
 17. Thenon-transitory computer accessible storage medium as recited in claim 14wherein the plurality of instructions, when executed, generate theinstantaneous acceleration factor from one or more operating parametersof the electrical device.
 18. A system comprising: an electrical deviceoperating responsive to a supply voltage during use, wherein theelectrical device includes one or more sensors that measure one or moreoperating parameters in the electrical device during use; a monitorcircuit coupled to receive the one or more operating parameters wherein,during use, the monitor circuit determines an instantaneous accelerationfactor measuring a current acceleration of end of life experienced bythe electrical device responsive to the one or more operatingparameters; and a controller coupled the monitor circuit, wherein thecontroller constrains operation of the electrical device responsive to adifference between a target acceleration factor and the instantaneousacceleration factor, wherein the target acceleration factor iscalculated to result in no more than a targeted failure rate of theelectrical device over a targeted lifetime of the electrical device,wherein the controller constrains operation of the electrical deviceresponsive to a history of the difference during use.
 19. The system asrecited in claim 18 wherein the history is gathered since a most recentreboot of the system.
 20. The system as recited in claim 18 wherein thehistory is gathered since an initial boot of the system.
 21. The systemas recited in claim 18 wherein the controller constrains a maximumoperating temperature of the electrical device.
 22. The system asrecited in claim 18 wherein the controller accumulates credit responsiveto the difference being positive during use, and wherein the controllerpermits less constrained operation responsive to the accumulated creditduring use.
 23. The system as recited in claim 18 wherein the controllerinitializes a credit during boot of the system, and wherein thecontroller permits less constrained operation responsive to the creditduring use.